Sandwich panels with a honeycomb structure body at the center thereof are used for walls and floors in airplanes, railway-vehicles and houses. Among the uses of sandwich panels, sound barrier material and sound absorbing material are important.
In this specification, a sandwich panel for sound barrier material is supposed as such provided with gas barrier layers on both sides and a piece of honeycomb at the center thereof, regardless of cells of the honeycomb being filled up or vacant. A sound absorbing material is supposed as such provided with gas permeable stuff at least on one side thereof, having cells of the honeycomb being filled up with porous material for attenuating sounds which make incidence through the gas permeable stuff. However, it is not certain, from person to person, whether a sandwich panel is called as a sound barrier material or a sound absorbing material.
Prior-art documents which may have some relationship with the present invention are raised below and explained briefly. The patent document 1 (JP-07-88995) presents an example in which cells of a honeycomb are filled up with some filler material. It discloses a structure body in which a honeycomb 2 and a sheet-like filler material 1 have the same breadths and widths. FIG. 1A of the present invention shows the same honeycomb - filler configuration shown in the patent document 1, and FIG. 1B of the present invention explains how the filler material drops off from the outer edge area of the honeycomb in the configuration shown in FIG. 1A.
The reason is that the six-sided cell walls located in the outer edge area of the honeycomb become opened when the cell walls are cut out, and the filler material can not be stably held there. When one wishes to produce a sandwich panel using the honeycomb structure body mentioned above, cutting the honeycomb structure body to fit the surface material is necessary. However, if the honeycomb and the filler material have the same dimensions, it can not be avoided the filler material from dropping off out of the outer edge area of the honeycomb due to above-mentioned reason.
Empty cells produced by the filler material that drops off deteriorate the barrier capabilities against sound and heat expected to the filler material, and damage the commodity value of the sandwich panel. Further, the filler material that have dropped off from the cells have to go to waste.
To prevent the filler material from dropping off, it may be possible to fix the filler material to the honeycomb with an adhesive agent. However, the adhesive agent will cause increase in cost and weight, besides work load, and in addition, it will cause to deteriorate the barrier capabilities against sound and heat of the sandwich panel.
The patent document 2 (JP-09-156010) discloses another invention, titled “Method of producing sound absorbing panel.” The described sound absorbing panel consists of a piece of honeycomb with empty cells, having a mesh layer over a perforated metal plate on each side of the honeycomb with a very thin film-like adhesive agent of thermosetting resin. However, the described empty cells differs from the definition of a sound absorbing panel.
The patent document 3 (JP-01-198951) discloses an invention titled “Method of producing panel-like core stuff.” There are described that a foam material is inserted into cells of a honeycomb with pressure, that an adhesive agent is applied to inner surface of the cells by dipping or spraying, and so on. However, no special precaution in application of the adhesive agent not to damage the gas permeability of the surface material is seen. In a drawing (FIG. 6) of the document showing an example, the adhesive agent is drawn as a plane (a horizontal line, in a section).
The patent document 4 (JP-Utility Model-61-30844) discloses a utility model titled “Sandwich panel,” in which a foam sheet having a thickness smaller than the height of a honeycomb is inserted into the cells of the honeycomb to the half depth of the cells. There are described that adhesion between the honeycomb and the surface materials is made at the end of the honeycomb, that the foam material can be melt by the adhesive agent, if the end surface of the foam material (polyurethane foam) comes to the level of the end surface of the honeycomb, and that unevenness of the surface material can be made in that case. However, no special precaution in application of the adhesive agent not to damage the gas permeability of the surface material is seen.